Diamond is the hardest material known; it has the highest capability to resist scratches. Carbon nanotubes, on the other hand, are the strongest structures known, and the amount of force they can resist, pound for pound, is the highest ever measured.

"There was this kind of 'what if,'" said researcher John Carlisle, a physicist at Argonne National Laboratory in Illinois. "What if you could integrate the strongest material known with the hardest known material? Would the sum of the parts be not only hard and tough, but maybe have other capabilities you wouldn't predict?"

The researchers grew their composite by exposing a surface covered with diamond nanoparticles and iron nanoparticles to an argon-rich, hydrogen-poor plasma. The diamond and iron nanoparticles catalyze the growth of ultrananocrystalline diamond and carbon nanotubes, respectively.

"For the most part we grow these materials onto flat surfaces, but the composite could also be more complex shapes, such as hip joints," Carlisle said.

The scientists published their research in the journal Advanced Materials.

The hybrid material could make for coatings as hard and low friction as diamond while less brittle. The composites might also find use in flat panel displays: The diamond may keep the carbon nanotubes from unraveling as they do normally when scientists attempted to make displays made from nanotubes alone. And the diamond-carbon nanotube material could also find use in bioweapons detectors, with nanotubes bound to biomolecules acting as the sensor elements and the diamond behaving as an exquisitely sensitive electrode.

By tinkering with the growth conditions, the researchers can vary the concentration, placement and orientation of the diamond and nanotubes, and then customize the composite's properties. Carlisle and his colleagues plan to spend the next few years analyzing the mechanical, electronic, thermal and other properties of each variation.

"This is interesting, exciting, and plausible work," said research chemist James Butler at the U.S. Naval Research Laboratory in Washington. "The impact of this work will depend on many factors unknown yet -- what are the properties of this material, what applications can benefit from, what will it enable, or what value added will it bring."

Robert Nemanich, a materials physicist at North Carolina State University in Raleigh, said an important aspect of the research "was the ability to control the relative amount of diamond and nanotube components of the film. This capability should enable engineering to precise materials properties for specific applications. This material should exhibit a wider range of physical and chemical properties than either diamond or nanotubes."

Most of the nanotubes in the composite are of the weaker multi-walled variety, but the scientists have detected the stronger single-walled kind as well.

"One of the short-term goals of our research is to minimize the growth of multi-walled carbon nanotubes in favor of single-walled carbon nanotubes," Carlisle said. "If successful, the fracture toughness of the composite will hopefully increase substantially."

It remains unclear as to how strongly the diamond and nanotubes are bonded together. The researchers also need to refine the growth process to make the composite reproducible.

"It will be a few years before we know whether the nanocomposites have sufficiently superior properties that would enable products with unique enough capabilities that justify their development," Carlisle cautioned.

The researchers have filed a patent on their results, which they have licensed to an Argonne laboratory startup company called Advanced Diamond Technologies.

Carlisle serves as chief technical officer for ADT in Champaign, Ill.

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Charles Choi covers research and technology for UPI. E-mail: sciencemail@upi.com

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